Production of alkyl aromatic hydrocarbons



Patented Feb. 24, 1948 UNITED s'rA'rEs PATENT OFFICE PRODUCTION OF ALKYLAROMATIC HYDROCARBONS Application March 22, 1946, Serial No. 656,471

9 Claims.

The invention relates to the conversion of hydrocarbon mixturescontaining paraffinic and aromatic components into higher boilingcompounds comprising alkyl aromatic hydrocarbons.

More specifically, it is concerned with a com-- bination of specificprocesses which individually involve the use of special catalysts andparticular conditions of operation whereby hydrocarbon mixturescontaining both parafhns and aromatics may be effectively converted intoaromatic hydrocarbons containing one or more alkyl groups attached tothe aromatic nucleus thereof.

It is one object of my invention to convert hydrocarbon mixturescontaining parafiins and aromatics into mono or polynuclear andsubstituted alkyl aromatic hydrocarbons, the particular product obtainedin the process depending upon the charging stock and the conditions foperation employed in said process.

Another object of this invention is to provide a highly efllcient andeffective process, characterized by little or no decomposition of thecharging stock and by the increased yield of desirable products, whichcomprises converting a mixture of paraflinic and aromatic hydrocarbonsinto alkyl aromatic hydrocarbons having `boiling points higher than saidcharging stock.

In one specific embodiment the present invention comprises a combinationprocess wherein a parafiinic hydrocarbon is iir'st dehydrogenated in thepresence of anv aromatic hydrocarbon and the product thereof issubjected to alkylating conditions to condense the olefins produced bysaid dehydrogenation with the aromatics to form an alkyl aromatichydrocarbon in which the alkyl group contains the same number of carbonatoms as said paraffin hydrocarbon.

Other specific embodiments of the present invention relate to theutilization of particular charging stocks, methods of operation and tospecio catalysts utilizable in said dehydrogenatlon and alkylationstagesy which variables will hereinafter be described in greater detail.

In the production of. alkyl aromatic hydrocarbons it is often desirableand in fact, in'some cases requisite, to produce said compounds underconditions such that the aromatic nucleus contains but one alkyl groupof the type desired per molecule. A typical instance in which suchcompounds are preferred is in the manufacture of alkyl aromatichydrocarbons for the production of the sulfonate type of detergents. Inthe latter instance the proper activity of the detergent product dependsupon the introduction of but one alkyl group into the aromatic nucleusprior to sulfonation and neutralization of the resultant alkyl aromaticsulfonic acid. lIn order to obtain hydrocarbons of this type it isAnecessary to employ a. process whereby the desired mono-alkylation isobtained exclusive of any polyalkylated product or, alternatively. toseparate the monoalkyl aromatic from a mixture'of the same with thepolyalkylated product obtained by conventional alkylation processes. Asimple expedient in 5 the economical production of mono-alkylates of thearomatic hydrocarbon is the utilization of a high molecular proportionof the latter compound in the alkylation reaction where such alkylaromatic hydrocarbons are obtained, The effect, therefore, of the highmolecular proportion of aromatic hydrocarbons to olenic hydrocarbons inthe reaction zone is to provide for a dilution effect whereby thepossibility of polyalkylation is substantially reduced because of theoperation of the law of mass action.

A further advantage to the use of an excess of the aromatic hydrocarbonsin the present combination process is that obtained by virtue of theheat carrying capacity of thearomatic hydrocarbonsin the dehydrogenationstage. In the dehydrogenation of parafilnic hydrocarbons to oleiinsrelatively large quantities of heat are consumed to effect saiddehydrogenation. I have observed that it is highly desirable tointroduce the necessary endothermic heat of reaction into the reactionzone by heating the hydrocarbon charging stocks prior to theintroduction of the latter into the reaction zone rather than attemptingto supply the required heat by externally heating the reaction zone.'I'he presence of a large proportion oi' aromatic hydrocarbons, whichare relatively stable at high temperatures and which have a high molarheat capacity in the charging stock to the dehydrogenation reaction,provides a means for supplying the required heat without resorting tothe alternative of heating the parailins contained in the charging stockto an excessively high temperature and thereby subjecting'the latter todecomposition, particularly cracking thereof. The latter factor, that isthe cracking of the parailins at high temperatures and in the presenceof catalytic agents of the composition employed for dehydrogenation, isespecially a factor of considerable importance when the parailin is ahigh molecular weight member of this class of compounds and isparticularly true for parafns of 6 or more carbon atoms.

The high proportion of aromatic hydrocarbons I contained in the chargingstock to the dehydrogenation reaction and also to the subsequentalkylation reaction enables the entire combination to be operatedcontinuously on a highly eilicient basis. The excess aromatichydrocarbons separated from the eiliuent product of said alkylationreaction are advantageously recycled in the dehydrogenatibn stagewithout any substantial L burden of separation since /the latterrionalkylated aromatics boil at reduced temperatures as compared to thealkyl aromatic hydrocarbons. so The charging stockin lthepresent-process, as

previously noted. comprises a mixture of parailns and/or cycloparalns(naphthenes) and aromatics, said mixture being either a syntheticallycompounded solution of the desired components or a naturally occurringmixture such as a straightrun petroleum fraction boiling, for example,within the gasoline range. If the latter charging stock is selected. thearomatic content thereof may be and is preferably increased \by addingthereto the preferred aromatic hydrocarbon since straight-run petroleumfractions, depending upon the source thereof, do not usually contain therequired content of aromatic hydrocarbons. Where the specific purpose ofthe process is the production of monoalkyl aromatic hydrocarbonscontaining a long chain al"yl group of 6 or more carbon atoms, themolecular proportion of aromatic hydrocarbons to long chain parans inthe charging stock is maintained at a higher value than in thecaselwhere the ultimate product contains a short chain alkyl group offrom about 2 to about 6 carbon atoms. In the latter instance, that is,in the production of alkyl aromatics wherein the alkyl group containsfrom about 2 to about 6 carbon atoms, the molecular proportion ofinitial aromatic to parain is held at from about 1:1 to about 170:1. Forthe production of alkyl aromatics having alkyl groups of from about 6carbon atoms and highern the proportion of aromatics to parafllns in theoriginal feed is gen-` erally held at higher values. above about 3:1.but

preferably above about 10:1 up to about 30:1,A

although the upper limit is also determined by balancing of economicalseparation of large quantities of aromatic hydrocarbons from theultimate alkylation product against the desirable.

production of mono-alkylated products.

Petroleum fractions containingy both paraffins and aromatichydrocarbons, usually of varying structure and molecular weight, areobtained in the straight-run petroleum distillates boiling in thegasoline and/or gas-oil boiling range. Preferably. as indicatedpreviously, additional quantities of aromatic hydrocarbons are added tosaid Y fractions in order to increase the aromatic content thereof abovethat normally present in the.

distillate. The resulting alkylate obtained by subjecting the product ofdehydrogenation to al ylating .conditions contains a wide variety oi'alkyl aromatic hydrocarbons.

Aromatic hydrocarbons utilizable in the process of the present inventioncomprise, in general, the alkylatable aromatics or, in other Words,those members of the aromatic hydrocarbon series containing asubstitutable position on the aromatic nucleus. Obviously, the processis inoperable as to aromatics having all the nuclear positions occupiedby non-substitutable groups. Thus, benzene and naphthalene areutilizable, as well as their mono, diand tri-alkyl derivatives, such astoluene, Xylene or other polymethylbenzenes, such as trimethylbenzene.It is also obvious that aromatic hydrocarbons which undergo reactionsforeign to the principal or desired reactions are not utilizable. Thus,vinyl aromatics which readily polymerize under the conditions employedherein or long chain a yl aromatic hydrocarbons which pyrolyze atrelatively low temperatures are likewise not to be included in the aboveindicated group of utilizable aromatic hydrocarbons.

Catalysts which accelerate the dehydrogenation of parafiln-aromatichydrocarbon mixtures to form a mixture of oleflns and aromatichydrocarbons suitable for subsequent alkylation comprise refractoryspacing agents or carriers selected from the group consisting ofactivated aluminamagnesia, silica and diatomaceous earth andminoramounts of the oxides of elements selected from'rnernbers of theleft-hand columns of groups IV. V and VI of the periodic table60nsisting of titanium, zirconium, cerium, hafnium \and thorium;vanadium, columbium and tantalum, chromium, molybdenum, tungsten anduranium.

The above dehydrogenation catalysts are normally utllizedvvattemperatures within the approximate range of from about 400 to about 650C., at atmospheric or superatmospheric pressures up to approximately 10atmospheres, and at an hourly liquid space velocity (dened, as employedin the speciiication and the hereinafter appended claims, as the volumeof liquid parafilns contained in the feed to the reactor per hour,divided by the superficial volume of catalyst in said reactor) of fromabout 0.1.to about 10. Conversion of the parains to olens ofapproximately to 30% per pass are obtained by properly selectingconditions within the above designated ranges. The time of contact em-25 ployed will vary greatly with the catalyst used, the temperature ofoperation employed and other factors, such as the time required forreactivation of the catalyst by removal of the carbonaceous depositsthereorn` formed during the dehydro- 80 genation reaction),l

The length of the operating cycle is ordinarily established by trial,since higher over-al1 results are obtained in continuous plants whenoperations are conducted for a relatively short interval followed by acorresponding short time of reactivation rather than when the catalystparticles are permitted to become contaminated excessively bycarbonaceous deposits.

The eiiluentproduct of dehydrogenation containing the aromatichydrocarbons charged into the latter reaction zone in substantiallyunaltered condition and the olelnic hydrocarbons formed bydehydrogenation of the paraiiins contained in the original feed ischarged into an alkylation reactor containing a suitable alkylationcatalyst and maintained at alkylating conditions which will cause thecondensation or said aromatic and said olenic hydrocarbons. Alkylatloncatalysts useful for effecting the reactions between the oleiinlc andaromatic hydrocarbons according to the process of this inventioncomprise sulfuric -acid (of from about 80 to about 100% or higherconcentrations, preferably an acid having a coneentration within theupper limit of said range),

phosphoric acid (usually the concentrated reagent containing a smallpercentage of the phos- .phoric acid anhydride), hydrogen fluoride(preferably of 95 to 100 per cent concentration), alumi- 5ynum chloride(anhydrous) with anhydrous hydrogen chloride, and a solid precalcinedcomposite of an acid of phosphorus and a siliceous' adsorbent, generallyreferred to as a solid phosphoric acid" catalyst.

For production of high yields of alkylate with- 05 out substantialdecomposition of the alkylation products through so-called destructivealkylation reactions when employing sulfuric acid, hydrogen uoride oraluminum chloride with hydrogen chloride as catalyst, the process ispreferably operated at relatively low temperatures, usually below about100 C. and under suiiicient pressure that substantial proportions of thehydrocarbons are present as liquids in the alkylation zone.

While the exact operating temperature for alkylation is dependent uponthe composition of the mixture being treated, which alkylation proceedsat a practical rate are approximately 45 C. when utilizing substantiallyanhydrous aluminum chloride with hydrogen chloride as the catalystmixture, at 50 C.

I others, the aromatic hydrocarbon such as benzene or toluene, forexample, is alkylated by olenic hydrocarbons at a temperature within theapproximate range of 150 to `375 C. under a pressure 'of the order of 50to 200 atmospheres producing thereby the desired alkylate.

Following the alkylation treatment, the total product, consistingprimarily of aromatic and alkyl aromatic hydrocarbons, together with theunconverted parains of the original charging stock is diverted to thealkylate separating zone in which the higher boiling alkyl aromatics areremoved by fractional distillation from the other components. Thefraction or fractions containing unconverted paraiilnsand excessaromatic hydrocarbons are recycled to the dehydrogenation stage andcombined with fresh feed charged to said latter stage, thus providingfor a continuous recycle of the unconverted portion of the feed,

For the purposes of illustrating the combination of steps characteristicof the present invention, the attached drawing shows diagrammatically atypical flow for producing alkylP aromatic hydrocarbons from a mixturecontaining 20 molecular proportions of benzene and one molecularproportion of normal butane to form monobutylbenzene.

Referring to the drawing, benzene is introduced through line l intodehydrogenation zone 2 containing a `catalyst selected from the abovementioned group of dehydrogenation catalysts supported on trays, if thereaction is of the xed bed type, or circulated in a finely powderedcondition, if the reaction is of the fluid type of catalytic/process. Aparaflinic hydrocarbon fraction containing butane separated as a natur1fleasoline fraction boiling at about C. is iiitro ced intodehydrogenation reactor 2 through line 3. The paraln reactant may bemixed prior to its introduction into the latter zone 2 with recyclestock containing excess aromatic hydrocarbon and unused paraflins, theorigin of which is hereinafter referred to in greater detail and whichenters line 3 through line I5. The mixture of aromatic and paralnichydrocarbons is contacted with a catalyst in dehydrogenation zone 2under conditions hereinabove specified for `the dehydrogenation ofbutane to butylenes in the presence of benzene. The eilluent products ofsaid dehydrogenation zone are removed through line 4 and are directed toseparation zone 5 where the products are separated into a normallyliquid hydrocarbon stream which is removed through line 6 intoalkylation zone 1 and a light normallygaseous product removed throughline 8 and discharged from the process. The light gases, consisting ofhydrogen formed in the dehydrogenation cf the paraiilns and light gasescomprising methane, ethane, ethylene and propylene formed bymiscellaneous reactions such as pyrolysis in the the lower temperaturesatv dehydrogenation zone, may be sent to storage or utilized as fuel forsupplying the required heat of reaction in the dehydrogenation stage, orthe hydrogen may be separated therefrom and recycled to thedehydrogenation zone through line 9 where it serves the purpose ofsuppressing carbon formation and cracking reactions.

The mixture of hydrocarbons containing benzene, unconverted butanes, andbutylene formed by dehydrogenation of said butanes is introduced intoalkylation zone I through line 6 where itis contacted with a catalystselected from the above specified group of alkylation catalysts suitablefor converting aromatic-olefin hydrocarbon mixtures into alkyl aromatichydrocarbons. In the case of a liquid alkylation catalyst, such asanhydrous hydrogen fluoride, sulfuric acid or phosphoric acid,alkylation zone 'I is equipped'with a stirring device suitable forcontacting the hydrocarbon components of the charge with the catalyst.Also, in the case of the above catalysts, as well as in the use ofanhydrous aluminum chloride-hydrogen chloride catalyst, a sludge phasecontaining catalyst-hydrocarbon complexes is ordinarily produced duringthe, alkylation reaction ,and this is removed from the process throughline Ill to a catalyst recovery process not illustrated in theaccompanying diagramvor to an incidental apparatus for the production ofby-products therefrom. The hydrocarbon product which ordinarily is anupper layer in the alkylation zone is removed therefrom through line IIinto separating zone ,I2 wherein' desired fractions of the alkylateproduct are separated from recycle fractions. Separation zone I2 is afractionating apparatus for separating the higher boiling alkyl aromaticproduct from the lower boiling recycle fractions. Said alkylated productis removed through line I3 while the recycle fractions are removed fromseparation zone I2 through line I4 and may be either diverted to asecondary separating zone for further purification before recycling tothe dehydrogenation zone or the fraction may be recycled directlythrough line I5 and admixed with the paraiiinic charging stockintroduced throughV line 3 and connected therewith. The recycle stockconsists of excess ben. zene not utilized in the alkylation zone to formthe alkyl aromatic hydrocarbons and unconverted butanes which, whenrecycled to the dehydrogenation zone into paraffin feed line 3 areordinarily roughly analyzed prior to their introduction into said zone 2to adjust the aromatic to paramn ratio charged into said zone to the,aforementioned optimum ratio of said reactants.

The following examples are included to indicate the nature of theoperation and results obtainable by said operation of the presentinvention, however; the data indicated therein are not intended toidenein any manner the limits thereof and are therefore not to beinterpreted' as restricting the broad 'scope of the invention inaccordance therewith.

Example I A mixture containing 12 molecular proportions of benzene and 1molecular proportion of normal butane is prepared and passed over adehydrogenation catalyst comprising a synthetically Acom-v sure ofapproximately 5 atmospheres and a gase lMabuse ous space velocity of 500are maintained through-,-

posite of kieselguhr and pyrophosphoric acid at a y temperature of 350C., a pressure ol 100 atmospheres and at agaseous space velocity of1000. The alkylation products are separated by fractional distillationinto a hydrogen fraction containing minor quantities of methane,ethylene and propylene, a fraction containing benzene and butane, and aproduct fraction containing butyl benzene and minor quantities ofdibutyl benzene, the total alkylate product comprising a nearlyquantitative yield based upon the weight o! butane disappearing in thereactor.

Eample II y A hydrocarbon mixture containing -18 molecular proportionsof toluene and 1 molecular proportion of a straight-run. petroleumdistillate boiling within the range of 160 to 250 C. and containingparaflinic hydrocarbons ofapproxl'- mately Cin- C12 chain length ispassed at a temperature of 500 C., at a pressure of 3 atmospheres and ata gaseous space velocity of 200 into a dehydrogenation reactorcontaining a catalyst similar in composition to the catalyst utilized inExample I above. The products of dehydrogenation are separated into anormally liquid fraction and anormally gaseous fraction, the lattercontaining hydrogen, methane, ethylene and propylene.

The normally liquid fraction separated from .the products o1dehydrogenation is passed directly into liquid anhydrous hydrogenfluoride at 20 C. and at 1 atmosphere pressure to maintain thehydrocarbons in liquid phase. An upper hydrocarbon layer separatedI fromthe products thereof after a reaction period of one-half hour is passedover alumina at 200 C. to dehydrolluorinate the hydrocarbons containedtherein. The resultant product is fractionated into toluene, a fractioncontaining the unconverted portion of the charged parafllns which islcombined with the toluene fraction and recycled tothe dehydrogenationstage, and a fraction comprising the alkylated toluene (decyl-dodecyltoluene alkylate, boiling from about 300 to about 340 C.).

The latter alkylated toluene when sulfonated under suitable conditionswith sulfuric acid yields an excellent hard .water detergent,

l claim as my'invention:

1. A process for the production of alkyl aromatic hydrocarbons whichcomprises contacting a mixture of an alkylatable aromatic hydrocarbonand a dehydrogenatable parafnhydrocarbon. said aromatic hydrocarbonbeing present in molecular excess over said parafn hydrocarbon, with adehydrogenation catalyst at dehydrogenating conditions to forman olefinhydrocarbon having the saine number ol carbon atoms per molecule as saidparailin hydrocarbon; contacting at least a portion oi the resultantdehydrogenation products, without further chemical treatment, with analkylation catalyst at alkylating conditions to alkyiate said aromatichydrocarbon with said olefin hydrocarbon; separating from the resultantalkylation `products the desired alkyl aromatic hydrocarbon and arecycle fraction comprising unconverted aromatic and paraffinhydrocarbons; and supplying said recycle fraction to the dehydrogenationstep.

2. The process of claim 1 further characterized n hourly space velocityof from about 0.1 to about in that the molecular ratio of said aromatichydrocarbon to said paraffin hydrocarbon in the feed to thedehydrogenation step is from aboutl 3:1 to about 30:14

3. The process of claim 1 further characterized in that undesirednormally gaseous components are separated from said dehydrogenatlonproducts prior to the alkylation step.

4. The process of claim 1 further characterized in that saiddehydrogenation catalyst comprises an oxide of an element selected fromthe lefthand columns of groups IV, V and VI of the periodic table andsaid dehydrogenating conditions comprise a temperature of from about 400C. to about 650 C., a pressure of fom about atmospheric to about 10atmospheres, and a liquid 5. The process of claim 1 furthercharacterlzedin that said alkylation catalyst comprises a'sold precalcined compositeof an acid oi phosphorus andasiliceous adsorbent 6. The process of.claim 1 further characterized in that said alkylation catalystcomprises substantially anhydrous hydrogen iiuoride.

7. The process of claim 1 further characterized in that said alkylationcatalyst comprises conceritrated sulfuric acid.

8. A process for the production of alkyl aromatic hydrocarbons suitablefor conversion to detergents by sulfonatlon and neutralization, whichcomprises contacting a mixture of an alkylatable aromatic hydrocarbonand a dehydrogenatable paraffin hydrocarbon containing at least 6 carbonatoms per molecule, the molecular ratio of aromatic hydrocarbon toparaflin hydrocarbon in said mixture being from about 10:1 to about30:1, with a dehydrogenation catalyst at dehydrogenating conditions toconvert said parain hydrocarbon to a monoolefln hydrocarbon having thesame number molecule as said parafn hydrocarbon; reacting at least aportion of the resultant dehydrogenation products, without furtherychemical treatment, in the presence of an alkylation catalyst at'alkylating conditions to alkyiate said aromatic hydrocarbon with saidmonoolenn hydrocarbon; separating from the resultant alkylatlon products(l) an alkyl aromatic hydrocarbon contain- REFERENCES CITED Thefollowing references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,143,493 Stanley et al Jan. 10,1939 2,287,931 Corson et al. June 30. 1942 2,349,045 Layng et al May 16,1944 OTHER. REFERENCES Ser. No. 390,534, Pier et al. (A. P. C.)published May 18, 1943.

of carbon atoms ,per`

